Feinstein, D-Calif., said, "The allegations against Senator Yee are shocking. It has become clear he has lost the confidence of his colleagues and for the good of his constituents should step down."

The senators' calls for Yee's resignation echo those issued by state Senate President Darrell Steinberg and other state senators on Wednesday following the news of Yee's arrest.

Yee's defense attorney, Paul DeMeester, said Thursday that Yeewas withdrawing his candidacy for secretary of state, but declined to comment on the criminal case or on whether Yee would resign his Senate post.

"We're taking one issue at a time," DeMeester said.

Yee, 65, a Democrat who represents the western half of San Francisco and most of San Mateo County, was arrested by the FBI on Wednesday on seven felony charges.

In a criminal complaint filed in U.S. District Court in San Francisco on Monday and unsealed on Wednesday, Yee is charged with six counts of scheming to defraud citizens of his honest services by allegedly soliciting and accepting campaign contributions.

The donations were allegedly in exchange for using his influence to aid a purported Mafia member, a business associate and another businessman in obtaining a state contract and medical marijuana legislation.

The purported Mafioso and businessmen were in fact undercover FBI agents,according to an affidavit filed with the complaint by FBI Agent EmmanuelPascua.

The contributions were for both the debt from Yee's unsuccessful2011 mayoral campaign and his now-dropped bid to be elected secretary ofstate in November.

In the seventh charge, Yee is accused of conspiring to traffic in firearms without a license, in connection with an alleged proposal to ship guns to a Muslim rebel group in the Philippines. The alleged plan was discussed with the undercover agent who was posing as a Mafia member, according to the affidavit.

Yee, a psychologist who previously served as a state assemblyman, San Francisco Board of Supervisors member and president of the San Francisco Board of Education, is one of 26 people named in the criminal complaint.

Others include Raymond "Shrimp Boy" Chow, 54, who is the current leader of the San Francisco-based Chee Kung Tong organization and who was previously convicted of racketeering and drug distribution conspiracy, and Keith Jackson, 49, another former school board president, who served as a fundraiser for Yee.

The charges include money laundering, drug distribution, trafficking in contraband cigarettes and trafficking in firearms without a license.

Jackson; his son, Brandon Jackson, 28, of San Francisco; Marlon Sullivan, 29, of Oakland; and Rinn Roeun, 30, of San Francisco, are also accused of using interstate commerce facilities -- namely, cellphone calls and text messages -- to promote a planned murder for hire.

The planned murder, which never happened, was requested by the FBI agent who pretended to be a Mafia member, according to the affidavit.

Most of the defendants, including Yee, made initial appearances before a federal magistrate in San Francisco on Wednesday. Yee was released on a $500,000 unsecured bond.

State Sen. Mark Leno, D-San Francisco, commentedon Yee's arrest and its effect on other members of the state Senate.

"We will get through this," he said at an event in San Francisco's Financial District this afternoon.

He said after learning about the charges he felt "disappointed, frustrated and angry."

Leno said he couldn't comprehend how Yee could be talking about protecting his community and children and families while allegedly working with international gun dealers simultaneously.

He echoed other elected leaders' call for him to step down from office and called Yee's decision to withdraw from the Secretary of State race "appropriate."

San Francisco Supervisor David Chiu said this afternoon that the 137-page criminal complaint "read like fiction" and the alleged wrongdoings of Yee are "disturbing" and "incredibly unexpected."